shopping framework

8/2/2019 Shopping Framework

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Java/XML-based Shopping Cart

Presented by

Mark Volkmann

[email protected]

Object Computing, Inc. (OCI)

2000 Object Computing, Inc.

All rights reserved. No part of these notes may be reproduced, stored

in a retrieval system, or transmitted, in any form or by any means,

electronic, mechanical, photocopying, recording or otherwise, without

the prior, written permission of Object Computing, Inc.


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Object Computing, Inc. Java/XML Shopping Cart2

Overview

Goal

create a prototype of a web-based shopping cart application that utilizes

Java servlets

XML and XSLT

HTML and JavaScript

Tools

Servlet Engine

Apache Tomcat 3.1

XML Parser

Apache Xerces - 1.1.3

XSLT Processor Apache Xalan 1.0.1

Java Development Kit

Sun JDK 1.2.2


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Screen Shots


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Screen Shots


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High Level Design

All client requests go through the GatewayServlet

The GatewayServlet directs each request to

a specific UseCaseController

A UseCaseController interacts with any number of

domain objects

Domain objects can populate themselves from databases

or XML documents

an improvement would be to move this functionality to other classes

that function as data adapters

Domain objects can create XML representations ofthemselves

an improvement would be to move this functionality to other classes

that function as data adapters


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Use Cases

View Inventory

display current inventory

allow user to enter item quantities desired

related files: ViewInventoryController.java, inventory.xsl

Add To Cart remove selected items from inventory

add selected items to users cart

invoke View Cart use case

related files: AddToCartController.java

View Cart

display contents of users cart

calculate total cost of cart including tax

done in XSLT stylesheet

related files: ViewCartController.java, cart.xsl


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Use Cases (Contd)

Remove From Cart

remove selected items from users cart

add selected items back to inventory

invoke View Cart use case

related files: RemoveFromCartController.java

Buy Cart gather information from user that is needed to process the transaction

includes name, address and credit card information

related files: BuyCartController.java, buy.xsl

Process Payment process credit card transaction

not actually done in sample code

display confirmation message

related files: ProcessPaymentController.java, purchase.xsl


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Interactions

Browser

Web Server

GatewayServlet

UseCaseController

Domain Object

Databases and

XML files

Domain Object Domain Object

UseCaseController UseCaseController


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Domain Objects

Item

holds a description, id, quantity and unit cost of an item

in the inventory or a user's cart

ItemCollection

holds a collection of Item objects Cart

extends ItemCollection

holds the Items currently in a user's cart

Inventory

extends ItemCollection holds the Items currently in the inventory


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Domain Objects (Contd)

Address

holds a street, city, state, country and postal code

used for user addresses

Person

holds the name and Address of a person

CreditCard

holds the name, number and expiration date of a credit card

Purchase

holds the Person, CreditCard, Cart and tax rate associated with a purchase


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Domain Objects (Contd)

Addressstreet : String

city : String

state : String

country : String

postalCode : String

Personname : String

address : Address

CreditCardname : String

number : String

expirationMonth : short

expirationYear : short

Itemid : String

description : String

quantity : int

unitCost : float

CartInventory

ItemCollectioncontents : Map

Purchasecard : CreditCard

cart : Cart

person : Person

taxRate : float*

1 1 1

1


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Controllers

GatewayControllerrun(ServletConfig, HttpServletRequest, HttpServletResponse) : void

AddToCartController

ProcessPaymentController

ViewCartControllerBuyCartController

ViewInventoryController

RemoveFromCartController


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GatewayServlet Overview

Creates a Map from use case names to

UseCaseController objects

only happens on the first request

mapping is described in UseCases.xml

more on this later

a use case name is passed as an initialization parameter to GatewayServlet

the use case name is a key in a Map of UseCaseControllers

this Map is placed in an HttpSession attribute so that

controllers can locate other controllers

useful when one controller needs to call another one

to finish processing a request

AddToCartController calls ViewCartController

after adding items to the cart

RemoveFromCartController calls ViewCartController

after removing items from the cart


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GatewayServlet Overview (Contd)

Looks up the UseCaseController that corresponds to

the requested use case name

Invokes the run method of the UseCaseController

This would be a good place to add

authentication

if the user has no current session then a login page could be displayed

authorization

GatewayServlet could restrict the use cases that a given user can execute


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HttpSession Attributes

Used to store

the UseCaseController objects

in a Map keyed on use case name

the Inventory

in a Map keyed on item id

a subclass of ItemCollection

the Cart

also in a Map keyed on item id

another subclass of ItemCollection


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UseCaseController Interface

package com.ociweb.framework;

import java.io.IOException;

import javax.servlet.http.*;

public interface UseCaseController {

void run(ServletConfig config,

HttpServletRequest request,

HttpServletResponse response) throws IOException;

}

ServletConfig provides access to the ServletContext which can be used to

read files in within the directory structure of the web app.

HttpServletRequest

provides access to form parameters andthe HttpSession object which contains a map of session attributes

HttpServletResponse

provides access to the Writer needed to send HTML back to the client

could also send WML

back to wireless devices


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ViewInventoryController Overview

This is the first UseCaseController that is invoked

If no Cart exists yet, it creates an empty Cart

If no Inventory exists yet, it creates an empty Inventory

and populates it

currently the data comes from inventory.xml

see next page

it really should come from a database

Creates a DOM Document object representing

the current inventory as XML

Transforms it to HTML by applying an XSLT stylesheet inventory.xsl


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inventory.xml

1

frying pan

39.99

5

2

spatula

4.99

7


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XMLUtil Overview

Provides static methods that make it easier to build

DOM XML Document objects

these return the new element so child elements can be added to it

Element appendChildElement(Node parent,

String childElementName)

Element appendChildElementWithText(Node parent,

String childElementName,

String text)



float value)



int value)


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XMLUtil (Contd)

Provides a static method that applies an XSLT stylesheet

to a DOM Documentvoid applyStylesheet(Document xmlDoc, String xslURL, Writer out)

void applyStylesheet(Document xmlDoc, InputStream xsl, Writer out)

Provides a static method that gets the value of a namedchild element within a given elementString getChildValue(Element element, String childName)

Provides static methods that pretty-print a DOM Document

void outputXML(Document doc) - sends to System.out for debuggingvoid outputXML(Document doc, OutputStream out)


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Mapping of Servlet Names to

Use Case Names

Tomcat web applications use web.xml to specify

servlet names and their initialization parameters

Each use case has a servlet mapping like the following

AddToCart

com.ociweb.framework.GatewayServlet

useCase

Add To Cart


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Mapping of Servlet Names to

Use Case Names (Contd)

There is one servlet mapping for each use case

All of them use GatewayServlet to service the request

An initialization parameter passed to GatewayServlet

identifies the use case being requested

Here are the URLs for running locally

using the default Tomcat port

http://localhost:8080/framework/servlet/AddToCart

http://localhost:8080/framework/servlet/BuyCart

http://localhost:8080/framework/servlet/RemoveFromCart

http://localhost:8080/framework/servlet/PurchaseCart http://localhost:8080/framework/servlet/ViewCart

http://localhost:8080/framework/servlet/ViewInventory


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Mapping of Use Cases to

UseCaseController Objects

Use case names are mapped to UseCaseController classes

by another XML file (UseCases.xml)

Add To Cart

com.ociweb.shopping.AddToCartController

Usage of this was described earlier

see page titled GatewayServlet Overview


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Sample UseCaseController(ViewCartController)

package com.ociweb.shopping;

import com.ociweb.framework.*;

import java.io.*;

import javax.servlet.*;


import org.xml.sax.SAXException;

continued on next page

used to produce the right

screen shot on page 3


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Sample UseCaseController (Contd)

public class ViewCartController implements UseCaseController {

public void run(ServletConfig config,

HttpServletRequest request,

HttpServletResponse response)

throws IOException {

Writer out = response.getWriter();

HttpSession session = request.getSession();

Cart cart = (Cart) session.getAttribute("cart");

XMLUtil.outputXML(cart.getXML()); // for debugging


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Sample UseCaseController (Contd)

try {

ServletContext context = config.getServletContext();

InputStream is = context.getResourceAsStream("/WEB-INF/cart.xsl");

XMLUtil.applyStylesheet(cart.getXML(), is, out);

} catch (SAXException e) {

out.write(e.toString());

}

}

}

reads file from the directory of the web app.

(in my case, C:\Tomcat\webapps\framework)


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Sample XSLT Stylesheet(cart.xsl)


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Sample XSLT Stylesheet (Contd)

Cart Contents

Select

Description

Unit Cost

Quantity

Total Cost

table headers

testing whether cart is empty

outputs a table row for

each item in the cart

sorted on description

uses template on page 31


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Subtotal:

Tax:

calculates the total before tax

calculates the tax


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Total:

Your cart is currently empty.

calculates the total including tax

one of the registered

servlet names

posts form fields

to form action


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outputs a table row for

the current cart item

see apply-templates on page 27


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Deficiencies in the Prototype

Controllers are dependent on the Servlet API

implementing controllers so they are unaware that they are

being invoked from a servlet is difficult

some controllers need to

access form parameters in the HttpServletRequest

send output to the client using information in the HttpServletResponse access and update session-level data in the HttpSession

read files in the directory of the web app. using the HttpContext


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Deficiencies in the Prototype (Contd)

Inventory persistence

the inventory is reloaded from an XML document

every time the servlet engine is restarted

the inventory is stored in a session-scoped object

so multiple users are not supported

one solution would to be to modify the Inventory class so that itinteracts directly with the database in every get and set method

as is done in a container-managed entity EJB


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Source Code

Complete source code is available in a separate zip file

ShoppingFramework.zip

setup steps are on the next page

Source code for couple of key classes follows


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Setup Steps

Here are the setup steps to run the provided code

installations

install Tomcat 3.1

install JDK 1.2 or 1.3

environment variables

insure that JAVA_HOME points to the JDK is installed insure that TOMCAT_HOME points to where TOMCAT is installed

copy framework.war to %TOMCAT_HOME%\webapps

modify %TOMCAT_HOME%\bin\tomcat.bat so CLASSPATH

contains xerces.jar BEFORE %TOMCAT_HOME%\lib\xml.jar

xml.jar is Suns Project X XML parser

start Tomcat point browser to http://localhost:8080/framework/servlet/ViewInventory


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GatewayServlet


import java.io.*;

import java.util.*;

import javax.servlet.*;


import org.apache.xerces.parsers.DOMParser;

import org.w3c.dom.*;

import org.xml.sax.*;

public class GatewayServlet extends HttpServlet {

private ServletConfig config;

public void doGet(HttpServletRequest request,


throws IOException, ServletException {response.setContentType("text/html");

PrintWriter out = response.getWriter();

config = getServletConfig();


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GatewayServlet (Contd)

HttpSession session = request.getSession();

Map controllers = (Map) session.getAttribute("controllers");

if (controllers == null) {

controllers = getControllers();

session.setAttribute("controllers", controllers);

}

String useCase = getInitParameter("useCase");

UseCaseController controller =

(UseCaseController) controllers.get(useCase);

if (controller == null) {

out.write("Fatal error: No controller found for " + useCase);

} else {

controller.run(config, request, response);

}

}


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public void doPost(HttpServletRequest request,


throws IOException, ServletException {

doGet(request, response);

}

private static Map getControllers() {

Map controllers = new HashMap();

ServletContext context = config.getServletContext();

InputStream is = context.getResourceAsStream("/WEB-INF/UseCases.xml");


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try {

DOMParser parser = new DOMParser();

parser.parse(new InputSource(is));

Document doc = parser.getDocument();

NodeList useCases = doc.getElementsByTagName("useCase");

int count = useCases.getLength();

for (int i = 0; i < count; i++) {

Element useCase = (Element) useCases.item(i);

String name = XMLUtil.getChildValue(useCase, "name");

String controller = XMLUtil.getChildValue(useCase, "controller");

Class controllerClass = Class.forName(controller);

controllers.put(name, controllerClass.newInstance());

}

} catch (Exception e) {

System.err.println(e);

}return controllers;

}

}


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XMLUtil


import java.io.*;

import org.apache.xalan.xslt.*;

import org.apache.xerces.parsers.DOMParser;

import org.apache.xml.serialize.*;

import org.w3c.dom.*;

import org.xml.sax.SAXException;

public class XMLUtil {

/**

* Note: parent must already be directly or indirectly appended

* to a Document before calling this.

*/

public static Element appendChildElement(Node parent,

String childElementName) {

Document doc = parent instanceof Document ?(Document) parent : parent.getOwnerDocument();

Element childElement = doc.createElement(childElementName);

parent.appendChild(childElement);

return childElement;

}


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XMLUtil (Contd)

public static Element appendChildElementWithText(Node parent,


String text) {

Document doc = parent.getOwnerDocument();

Element childElement = doc.createElement(childElementName);

parent.appendChild(childElement);

Text textNode = doc.createTextNode(text);

childElement.appendChild(textNode);

return childElement;

}


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XMLUtil (Contd)



float value) {

return appendChildElementWithText

(parent, childElementName, String.valueOf(value));

}



int value) {

return appendChildElementWithText

(parent, childElementName, String.valueOf(value));

}


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XMLUtil (Contd)

public static String getChildValue(Element element, String childName) {

Node node = element.getFirstChild();

while (node != null) {

if (node instanceof Element &&

node.getNodeName().equals(childName)) {

return node.getFirstChild().getNodeValue();

}

node = node.getNextSibling();

}

return null;

}


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XMLUtil (Contd)

public static void outputXML(Document doc) {

outputXML(doc, System.out);

}

public static void outputXML(Document doc, OutputStreamout) {

OutputFormat format = new OutputFormat("xml", "UTF-8", true);

format.setIndent(2);

XMLSerializer serializer = new XMLSerializer(out, format);

try {

serializer.serialize(doc);

} catch (IOException e) {

System.err.println(e);

}

}

}

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